Process for the production of potassium and magnesium sulfate double salts



INVENTOR ATTORNFY Naw: mw .Om um April 7, 1959 H. AUTENRIETH 2 881 050 PROCESS FOR THE PRODUCTION OF POTAssIuM AND MAGNESIUM sum/.TE DOUBLE: sALTs Filed Oct. 20. 1955 2 Sheets-Sheet 1 vom? Aprn 7, i959 1 H. AUTENRIETH 2,881,050 PRocEss FOR THE PRonucTIoN oF PoTAssIUM AND MAGNESIUM SULFATE DOUBLE sALTs Filed Oct. 20. "955 2 Sheets-Sheet 2 duz on hh Gm.

INVENTOR HANS AUTENR/ETH BY um gn LUIK] ATTO EY United States Patent 2,881,050 PRocEssFoR'THE'PRoDJCoN'oF'PoTAssIUM AND MAGNESIUM'SULFTETDAOUBLE SALTS Hans Auteuriethy-Hannover, 1 Germany,'assignor to Veff' kaulsgemeinschaft Deutscher Kaliwe'rlre` G.m.b.H., Hannover, Germany,.a,corporaton of Germany;`

Applicationfocte'r'20,11955; serial imif'siilhstl 211 .'olim" a, (ellas-117) `l` The present inventionffrelates to a nov'el methodv for the production of potassium ,fandma'gn'esium-sulfate dou# ble salts.v More particularly;,thetiriventionrelatestov av` process for the -productionof hyd'ratesofy double saltsof potassium and magnesium ff sulfate,` both, starting from'- containing sodium chloride' or'V initial materials either free of sodium chloride; and, simultaneously therewith,

the recovery of substantial:quantitiesfot magnesium chloy ride from the double salt.: conversion solutions;

It is wel1knownltthatf;in"theproduction-of potassium and` magnesiumA sulfate doublesalts; #the :higher .f the con tent of magnesium 'chloride iwi-thin thesolutions' used Lto obtain the'double-zsalts,hereinafter referred` to as :conf

larger will be 'the output-of vtheversion solutions, the

double salt; itselfpxdnv-addition;1 it'liswell knownthat a relatively high fconte'nttof-magnesium--chloride infsuch conversion solutions rwill 'makefor-a more economical over-all-process,/sincemagnesium chloride itself can` be' recovered and used- 1 for :the vvmanufacture Yof magnesium oxide t and hydrochloric acidiyThus, vthe Vartt-recognizes onV the one hand the znecessitytor `obtaining fhigher yields of the kdouble salts.-tthemselvesffand,y onthe otherv hand the desire to obtain-raconversion'solution:possessing-Eav highl y content fof magnesiunr chloride: I

With respect to prior known processes, the fusual v-yieldof the double salu-calculated "ont the basisoff-KZO, varies from approximatelyv 63478%3v of theoretical Atthe' same time, vit hast .beenapossibleto produce' conversion solutions containing-magnesium;chloride in agfcontentof approximately".38445mo1s/1'1Q000-mols of H2O at best,

One object ofwthe presentinvention-'Lis 5 the production.4

of doublev'salts 1otwpota'ssiuma:andmagnesium lin better yields. than .it fwasheretofore t-possible.y

Another l object of the invention fist-theproduction ofl said double -saltss fromsolutions :containing l sodium chloride (saturated ortnotsaturated);v in better yields than wasvheretoforefpossible,

A third-object of Y.the,finventionfislthe.recoveryrof a mother liquid -havingasubstantia1ly,higher concentration of magnesium chlorideffromaconversion solutions used ,in

the productionof-vsuchl'potassiumimagnesium double salts.

These, andmfurther-:objects of the v.invention willribe-` come 'apparent in-the-description thereof, read iny con junction withwthe drawings,in whichr. v

Fig.1 is a graph'showingfyariousbands of isotherrnsof at stable and meta-stable'solubilities in accordancetwith the-invention, excluding the presence of sodium chloride; this graph represents at any point complete 'saturation with potassiumchloride; andff` i N Fig..2- is aA graphfsimilar'toigi'l, butin'clding' the' 2,881,050 Patented Apr. 7, 1959 presence' l of sodium :-chloride,- ,iter inv the .wholegraph`vexists @complete 1 saturation 'no tvonlyf with potassiumfchlo-v.

ride -butalso withfsodium chloridef (The me'thodsffor `the graphical representation ofV corriplexv` salt-systemsfiwere-:developed Aby" DAns: Die

Ls'ungsgleichgevi'fichtey d er Systeme derK Salze-ozeanis1 cherv Salzablagerungen-. Berlin, 1933,-pages 13-44.- Also the 'methodf of t the r Parallelprojektiod there,- p.- 32 and w following.Y Our= graphs.' are: cuts through the three f' dimensional iso'the'rms,Jv as'v -itis -f deseribedr bybDAns on ,Unter suchungen ber die metastabile'Lslichkeit in-Sy 'stemen. der.v Salzenozeanischer 'Salzablagerungenf Kali 38 (1944),lpages 42^-49',6973, 86-92.)

' As contrasted t withv prior conventional procedures*l as4 outlinedv above, in accordancel'with'the instant Yinvention, it is 'now'possiblento'obtain' yields ofthe double"y saltcalculated-asfK'zO of 89% andf above, which is an increase of at least 10-25% as compared with prior conventional processes. i Atwth'elsam'e time, the yields of magnesium chloride'obtained from the conversion solutions range vcorrespondingly exceedingly higher, i.e.','

50 and above mols/ 1,000' mols'` of "HZO ,corresponding- `In order` tov better'-` understandI the-op`erationfoff-the`- instant invention,` reference isvr madeinitially to'Fig l' of the' drawing.r Asr'vis stated=thereon,l the solid linesv relate to stable'fconditions of equilibrium, while the dotted vlilies anddashed linesrelate' to 'meta-stable-con A system consisting" of i a-solutionfand 'one'or-more sediments'is lcalled -stable if, `provided that external con-- ditions'frem'ain unchanged,4 the vcoi'n'positionofthe solu' tion'a.nd 'of existing' sedirnentsedoesy not change even during 'an infinite period of times A system consisting" of la solutionand one `or more sediments is calledv nietalstalsleifr'thesolution is oversaturated withone or several salts-fand if this or -t-hese-l salts which :exist i in =oversatu`ration inthe solution, -fdo not occur as`-sedini`ents;. insteadfone orseveralothers,-

whichlata giventemperature and given 'conditions' ofride #and magnesiumv sulfate and hydrates thereof at a' conversion temperature'of 15 C., it shouldbe possible to yattain the stable point 'of equilibrium indicated'by M150, which vis shown vonv Fig.- 1 and at which point KCl, schoenite and Epsmsalt (MgSO47H2O) willcoexist, and further, at which vpoint the conversion solution` should have a contentof r50.7 mols of MgCl2/ 1,000' mols of H2O corresponding t'o 241 g./l. MgCl2. Furthenfor example, on'the '25 Lisotherm kof schoenite, thek point K25 should beobtaina'ble, at' which point KCl, schoenite,

leonite, and kainite should bein co-exis'tence, while, at the same time the convesionsolution should contain 52.0 mols of MgCl2/1,000 mo1s-'o1'H2OL (243 g./l. MgCl2).

The metastable solubility of leonite and the stable soluis* given l representatione of the bility of schoenite converge at this p oint., Also the kainite forms a stable solid phase at this point (line of solubility of kainite for this temperature is not drawn). The same applies to KCl:four salts point.

As is quite obvious, the amounts of MgCl2 described above with respect to points M and K25 are in fact greater than any amounts of MgCl2 attainable in conversion solutions in accordance with prior procedures. The relatively high contents of magnesium chloride in conversion solutions has not beenattainable in prior art processes, however, because of the fact that the hydrated magnesium sulfate employed in the production `of the double salt possesses an extremely slow dissolution rate at the given temperature when approaching its saturation point of solubility. Thus, if it were sought to saturate the solutions with hydratedmagnesium sulfates in order to produce the double salt at the required temperature as shown on the isotherm, the time required for the reaction would make the process economically and practically impossible.

In addition, were an excess of hydrated magnesium sulfates thereof applied at the given temperature in order to accelerate the conversion, the result would necessarily be an excess of Epsom salt in the double salt itself, which is recovered, thus seriously aecting the purity of the double salt, and, in fact, preventing this mode of operation.

In accordance with the instant invention, however, it was discovered that in the system of the saltpair KCl+MgSO2=K2SO4+MgCl2 it was possible to attain the various points of equilibrium on the isotherms, as, for example, the stable point of equilibrium M150 without the necessity of an overly long period of time expended in dissolving hydrated magnesium sulfate on the one hand or the use of a large excess 'of hydrated magnesium sulfate on the other hand. In accordance with the invention, moreover it is now possible to carry out the conversion of the potassium chloride and hydrated magnesium sulfate into the double salt in the meta-stable eld exclusively, wherein it is possible to obtain conversion solutions having an exceedingly high content of magnesium chloride.

Thus, the process of the application in general contemplates the reaction of Epsom salt with potassium chloride carried out at a temperature suiciently high so that, in accordance with the graphs set forth in Figs. 1 and 2, the conversion solution will not be saturated with Epsom salt. The double salt formed during the reaction already segregates during this process and after all the Epsom salt is completely dissolved, the solution is cooled down sufiiciently to precipitate further quantities of the double sulfate of potassium and magnesium therefrom, and thus, in fact, the desired point of equilibrium in which the potassium chloride, the Epsom salt," and for example, the schoenite, co-exist, is attained. The precipitation of KCl and Epsom salt takes place only, when the temperature of the solution becomes lower than the temperature for which the initial quantities are calculated. In consequence the desired double salt is recovered in the particularly pure form, since there will be no surplus of Epsom salt or potassium chloride therein, and, at the same time the conversion solution is saturated with KCl, Epsom salt and the double sulfate, and very substantial quantities of magnesium chloride may be recovered from the conversion solutions and further used for various chemical processes.

Referring for the moment to Fig. 1, it is seen that isotherms for schoenite at 15, 25, 30, and 35 C. are given and, at the same time, isotherms for Epsom salt within the same temperature range are given. Attention is called to the line formed by connecting the points of connection of the schoenite and Epsom salt isotherms of similar temperature. This line, the polytherm so formed, is classied as a line of co-existence of KCl-l-schoenite-l-MgSOy 7H2O sented in Fig. 1 by the line connecting the points M150, M2250, M25", Maut), and Ms5 Similarly, in Fig. 1 lines of solubility are shown for the double salt leonite (MgSO4-K2SO4'4H2O), which does not appear as solid phase below 25 C. While the lines of the metastable solnbilities are represented for 25, 30 and C. (dotted lines), from the stable solubilities only that for 35 is given (full line). By connecting the points of intersection of the isotherms of leonite on the one hand and the isotherms of Epsom salt on the other hand (points L25, L20, L25) the line of coexistence of KCl-l-leonitc-l-Epsom salt within the temperature range of 25-35 could be obtained in the same manner as the schoenite line (leonite line not drawn in Fig. l). Similarly, therefore, when seeking to lproduce leonite, the reaction solution is cooled down to a point for which the quantities of initial ingredients are calculated with the leonite thereupon being recovered from the reaction solution. The double salt leonite, which is recovered in this manner, is, by the samereason-as with schoenite, as described above, of a particularly pure quality, since there is no excess of either Epsom salt of KCl therein.

The saturation lines of kainite have been omitted (except the 22.5 C.-isotherm) from Fig. l, since within the practical field of operation as set forth therein kainite will have only a very low rate of formation, and thus does not come into question in the separation of the double salt.

As may be seen from Fig. 1, ata conversion temperature of 30-40 C., one would operate within a field wherein schoenite is in a meta-stable solid phase. Under these conditions, the stable solid phase (within the particular temperature range) is the leonite. However, leonite has a much lower rate of formation than schoenite, so that under these given conditions, only schoenitc will be segregated and separated.

In addition, the stable point of equilibrium K25, which represents a point of co-existence of KCl-i-leonite-l-schoenite-l-kainite, may be obtained in accordance with the invention by at lirst carrying out a conversion with prescribed quantities of KCl and hydrated magnesium l sulfate as wouldbe theoretically required to obtain the point K25 within the temperature range of about 30-40 C. After the hydrated magnesium sulfate has been dissolved, a cooling of the reaction solution to a temperature of about 25 C. would take place, and the desired results obtained.

As is quite evident, Fig. 1 shows the additional possibility of obtaining meta-stable conversion solutions which have exceedingly high contents of magnesium chloride. For example, the conversion solution obtainable at the point M250, which is a saturation of KCl-l-schoenite-l-Epsom salt at a temperature of 25, is readily obtainable without any particular ditliculty, even though the conversion solution at this point is super'saturated with leonite and kainite. Under the conditions prevailing, however, both solid phases of leonite and kainite present in supersaturation have such an insgnicant tendency of formation, i.e., tendency to precipitate and/or segregate, that they cause no diculty whatever and a very pure double salt without any admixture of Epsom salt and KCl is obtaiuable. The conversion solution at point M25 has a content of magnesium chloride, on the other hand of 54.7 mols/ 1,000 mols of H2O, which corresponds to 256.5 g./l. MgCl2. Similarly, when operating with an equilibrium solution at M309, a highly purified double salt without admixture of Epsom salt and/or KCl is obtainable, and at the same time a content of magnesium chloride in the conversion solution of 56.0 mols/1,000 mols of H2O, corresponding to 260 g./l. MgCl2, may be recovered.

It may be further seen from Fig. 1 that the points of coexistence, L25, L30", and L35, in which KCl, leonite and Epsom salt co-exist, are situated within a particularly desrablc range with respect to MgCl2` recovery, since the conversion solutions Withinthis range show a much higher concentration of MgCl2 than any of the previous mentioned conversion solutions. lhighly desirable magnesium chloride solutions along with In order to obtain these the simultaneous production of a desirable double sulfate; it is important to provide that leonite and not schoenite is obtained as the double salt, and, at the same time, that separated exclusively.

Thus, in order to obtain theconversion solution atthe point Lan, With its magnesium chloride content of 61.1

mols/1,000 mols of H2O, corresponding to 285 g./l. MgCl2, one would stir at temperatures of rabout 45-55 C. quantities of Epsom salt, or other hydrated magnesium sulfate, potassium chloride, and water, as would be theoretically required for the double salt conversion.

After the Epsom salt has been dissolved, the solution should be cooled to about 30 C. At lirst, the conversion will proceed within the temperature range of about ll5-55 C., wherein only leonite is formed. When there is a cooling down to about 30 C., the magnesium sulfate in solution reacts with the remaining potassium chloride present, and further quantities of leonite` are segregated. The presence of the solid leonite formed in I the solution at the temperature between about Ll5---55 C., causes that also at temperaturesbelow 45A exclusively vleonite and at no'time schoenite is segregated. .In this Umanner, the'equilibrium solution Laofl is attainable and,

at the same time, a completely pure double salt (leonite) is recovered.

It is possible to operate within the entire rangeL-25-L350 .and to recover the magnesium chloride conversion solution all along this range. However, when operating here,

. it should be noted that from a practical standpoint it is not expedient to attempt to produce conversion solutions having contents vof magnesium chloride much higher than vthe contentpresent in the L30 solution, because when working above this point, there is-ever present. anfimminent Vdanger of kainite" formation.

, In addition, in this operation aswith the various other operations in accordance with the invention, in placeof water in the formation of the conversion solution, i.e.,

Epsom salt, potassium chloride,.and water as.v prescribed above, it is possible toemploy a quantity of a solution equivalent to the theoretical quantity .of waterV required, this solutionhaving present a low content of magnesium chloride, which solution may be obtained, lfor example, from variouschemical manufacturing processes, Includving conventional processes forthe production of double sulfates wherein a solution with a `low content of magnesium chloride would be present.

The various systems as discussed aboveln conjunction with Fig. 1, relate to a system free of sodium chloride,

i.e., the supposition that all starting products used in the conversion are free of NaCl. In fact, it is well known that the cost of sodium chloride-free potassium 'chloride is far in excess of potassium chloride having a 'certain content of sodium chloride therein. 'In fact, the

purity of commercial potassium chloride will not permit its use in the system free of sodium chloride as described in Fig. l. In View of this, an analagous gureto Fig. 1, i.e., Fig. 2, was prepared, which shows the conditions of solubility of sulfate saltsl within the region'saturated with sodium chloride and potassium chloride, and," in fact, relates to the production of double salts :of potassium and magnesium sulfate produced in avsystemrin which sodium chloride maybe present, either in part or# to saturation.: .The.various'ldesignationsl int Fig. l2"'are, asobviously set-forth,` quitezsimilartothoseof'Fig. 1,

f .the'continuous-lines' referring to-equilibriumof salts in the stable field,- while the dotted fandI dashed lines-relate to meta-stable conditions. Y

v The preparation` and operation ofthe process is exactly -the same'withv respect-towFig. 2 a's with-Fig. 1,'as--described above.

' A comparison of Figs. land 2Yshowsthatthe'line of coexistence of Epsom salts and schoente,` in the system v saturated withvsodium-chloridc (Fig. 2') -willy shift towards substantially lower-values of magnesiumchloride in the conversion solution, vas shown,forlexample,.byfthe line chloridel shown: in =Fig. l.

`. vThe information set-forthinl-Tigs. liand- 2,I therefore,

,obviously maybe very. advantageouslye'mployedin the formation" ofconversion solutions containing magnesium chloride in asystem containing'orsaturated lwith sodium chloride. It is-seen'that the lines of saturation ofEpsom .salt in both systems (Fig. Alaand Fig.,2) are almost completely similar withinthe -eld of operationshown. Thus,

. ifschoenite is sought tobe produced from Epsom' salt '35. On the other hand, lwhen leonite is produced 'fromEpsom hydrated magnesium sulfate and f vand potassium-chloride wherein a sodiumchloridesaturation is additionallyl present, the conversion'solutionsobtained in accordance'w-ith Athis procedure willnot contain too much magnesium chloride, and, infact, willvnot contain much more than-50 mols of -MgCl2/ 1,000 molsfof H30, corresponding `to `225-230-.g./l. MgCl2-at best.

saltand potassium chloride in a system saturated with sodium chloride, theconversion solutions will `have a contentofmagnesiurn :chloride just about Vequal to that obtained in a vsimilarconversion in a system-freerentirely from sodium chloride.

The production of double salts and conversion solutions containing ysubstantial quantities of magnesium chloride is basically the same in the system saturated with sodium chloride as in the system free from sodium chloridel previously described, with the exception that the tendency of formation of the double-sulfate salts is shifted toward lower temperature ranges. Thus, whentoperating in a system saturated lwith sodium chloride, and seekingto produce schoente, a temperature of 35l C. should not be exceeded, while simi1arly,- when seekingto produce leoniteVin the system saturated with sodium'chloride, a temperature of 50 C.. at` most should vbe-employed.

Therefore, in themodeof operationwhen seeking-to .obtain schoenite and the solution M25"` in accordance yand. 'after dissolvingallthe Epsom salts present; the conversion solution is thencooled 'downto'about 25 .'C.

. Similarly, when seeking to producelenoite and-the conversion solution at-point L'25 inl accordance with Fig. 2,' the required quantities water theoretically required for the conversion are stirred at a temperature of about y45 C. until all the magnesiumsulfate hydrate has" been dissolved, and thereafter the' mixture is cooled to a temperature of about 25 C., wherein a conversion solution having a composition of magnesium chloride'of 57.3 mols/ 1,000 mols of H2O, corresponding to about 265 g./l. MgCl2, is produced.

' In' the various conversions set forth above, inl-place of of potassium chloride,

Epsom salt (MgSO4-7H3O), dehydrated Epsom salt or dehydrated kieserite may also be used. In this connection, it has been found that the best mode of operation is to initially stir the quantity of dehydrated magnesium sulfate theoretically required for the conversion at a temperature of say from about 35-40" C. in the aqueous medium, whether it be water or a liquid having a. low content of magnesium chloride. The magnesium sulfate is added at this point without the addition of potassium chloride, and this addition increases the temperature of the aqueous medium to approximately 60 C., due to the heat of hydration of magnesium sulfate. Thereafter, a cooling of, for example, to about 45-50 C. is effected, and only at this point is the potassium chloride required for the conversion added, the KCl and MgSO4 thereupon reacting to produce leonite. Thereupon the mixture is cooled down in the prescribed manner to about the temperature for which the initial ingredients have been calculated. The desirability of employing this particular mode of operation when employing dehydrated magnesium sulfate lies in the fact that the heat of hydration upon dissolving the magnesium sulfate causes an increase of temperature to more than 50-55 C., and if the solution were saturated with potassium chloride at this time, there would be a substantial danger of the formation of kainite and a subsequent interference in the proper operation of the procedure. However, when adding the KCl after cooling the initial solution of dehydrated magnesium sulfate in the aqueous medium, there is no danger of the formation of kainite.

In addition, when producing a double sulfate in accordance with either Fig. 1 or Fig. 2, it is possible to obtain even greater values of magnesium chloride in the conversionsolution. Thus, after producing and separating the double salt from the conversion solution saturated with Epsom salt, it is possible to further cool the conversion solution in order to precipitate a mixture of Epsom salt and potassium chloride or Epsom salt, potassium chloride, and sodium chloride, as the case may be, in any event, further increasing the content of magnesium chloride in the conversion solution itself.

This further cooling procedure is shown graphically,

for example, on Fig. 1, wherein the crystallization path when cooling the conversion solution at point M250 from 25-l5 C. is shown, the path cutting the Epsom salt isotherm of C. at point E15". As is seen, the conversion solution existing at point E150 has a substantially higher content of magnesium chloride, and thus Ia correspondingly lower content of potassium chloride than the solution at point M250. The mixture of Epsom salt and potassium chloride or Epsom salt, potassium chloride and sodium chloride which will crystallize and separate out due to the cooling of the conversion solution from 25-15 may be returned to a further process for the production of double salt after separation from the conversion solution itself. It is essential, however, in-this procedure that, prior to cooling from the desired initial point, i.e., M250 in the instant case, the double salt be removed from the conversion solution. Otherwise, as is quite evident from Fig. 1, the double salt produced would react with the magnesium chloride of the conversion solution forming potassium chloride and Epsom salt, and thus in elect reversing the reaction and producing a solution having a low content of magnesium chloride. The possibility of carrying out the production of the double salt with an aqueous medium initially containing some quantities of magnesium chloride instead of pure water, has previously been mentioned. Such an aqueous medium may be obtained from the production, for example, of potassium sulfate, or a conventional double salt production wherein low magnesium chloride conversion solutions are obtained, or from any other chemical process, and the production of the double salt is preferably eiected in such aqueous medium containing small quantities of magnesium chloride.

In addition, a two-stage process of operation in the production of the double sulfate is effected in various twostage processes, some possibilities of which are as follows:

A conventional double sulfate process is initially effected whereby a low-content magnesium chloride conversion solution is obtained and this low-content conversion solution is once again reacted with magnesium sulfate, either hydrated or dehydrated and potassium chloride in order to produce the double salt and the high content MgClz conversion solutions.

In addition, the two-stage process may be in each stage a production of a double salt in accordance with the invention, as, for example, producing schoenite in the rst stage of conversion, and leonite in the second stage. Such an operation is advantageous in that a large portion of the double salt produced is in the form of readily tiltera-ble schoenite, and the second stage results in the production of only a small percentage of the total of the double salt produced in the form of the less readily filterable leonite, while the conversion solution itself has an extremely large content of magnesium chloride. If so desired, this procedute may be reversed, and leonite produced in the first stage and schoenite in the second. Further, it is, of course, possible to effect -a two-stage reaction wherein either schoenite or leonite is produced exclusively in both stages.

When operating with potassium chloride containing substantial quantities of sodium chloride, or if the initial aqueous medium employed contains substantial quantities of sodium chloride, it is always possible that the double salts produced will contain some solid sodium chloride when separated. This will be true in any case where the conversion solution itself cannot absorb and dissolve all of the sodium chloride present in the process. A separation of the double salt produced from solid sodium chloride contained therein will be effected in accordance with various conventional procedures, flotation being preferred in such cases.

Where a production of double salt is effected with solutions which contain sodium chloride, but which are not saturated therewith, the prescribed points of operation for the desired conversion solutions may be readily calculated by linear interpolation between the graphs shown in Fig. l (no NaCl) and Fig. 2 (saturated NaCl).

For practical purposes it is expedient not to cool the mixtures exactly to that temperature at which the double salt is in a state of equilibrium with Epsom salt and potassium chloride or with Epsom salt, potassium chloride and rock salt, but only to a slightly higher temperature. By this means undercutting of the temperature of equilibrium and consequently the danger of reforming of Epsom salt and potassium chloride from the double salt is definitely avoided at the secondary treatment (iiltration etc.).

For the production of leonite preferably a range of temperature between about 25-35 C. is chosen, for the production of schoenite one between 20-28" C. Said ranges of temperature may be selected in the presence of NaCl as well as in its absence.

Table l, appearing below, contains the equilibrium data of the various conversion solutions defined and shown in Figs. 1 and 2.

TABLE l Solid phases with which the solutions are ina state o! No. tion of solution KCl+schoenito+Epsom salt (stable). KCL-i-sehoenite-l-Epsom sait (meta).

COMPOSITION "OFEQUILIB RIUM" SOLUTIONS Mols/1,000 mols of H G. 1. No. Specific l weight MgCl: MgSO( KzCla N 8.2012 MgCl, MgSO4 KCI NaCl 50. 7 11. 5 8. 3 1. 270 241 69 62 54.7 15.3 8.5 1.295 256.5 90.5 62.3 56.0 17.8 8.9 1.3075 260 104. 5 64.7 56.0 14.9 8.2 1.297 262.5 88.2 1 60.2 61.1 16.1 7.7 .1.3195 285` u 95` 56.3 49.5 16.9 8.3 8.4 1.309 228 99 f 60l 50.9 19.6 9.0 7.8 1.321 -233 '113.5 64.4 57.3 15.0 7. 0 6. 2 1. 312 265 J 87. 3 50.6 58. 8 15. 8 7. 2 5. 8 1. 318 271 f 92 52 The following examples describethe yactual procedure;

for the production of the double. salts along with the various quantitative conditions employed; these examples are illustrative. only..and are. not.intended inv any lway to limit the generic scopey of y.the invention. as .covered-,by the lappended claims.

Example l Production of schoenite in a systemffreeY from NaCl, using KCl, Epsom salt and water:

vThe conversion solutionfMgS-in accordance with Fig. 1 s obtained. The quantitative conditionsare calcu' lated according to the following equation:w(quantities are indicated as mols or double mols) `The production of 1t schoenite requires:

0.428tKCl, 1.395t,Epsom salt and 0.3741* water.` A.The

. initialv products are stirredat a temperature of'about l -40" C., using the quantities indicated until the whole of the Epsom salt has been dissolved.V Thishappens after .about half hour. Afterwards the` mixture is'cooled down to about 25"` C. and the schoenite is separated from the adherent liquor by iiltrationf The KZO yield is 8615 the 1 S04 yield is 87.7 By cooling the mother liquor from 25.to 15 a mixture of Epsom salt and. potassium' chloride is segregated, which may be usedforother chargesIThe v.,KzO ryield istherebyincreased to 89.5, the SO4'yi'eld to Example 2 lProduction of leonite inthe system saturatedwith NaCl,

l. using a mixture of KClzand NaCl, :Epsomsaltfand water; the conversion liquor. L'25 is" obtained in accordance vwith Fig. 2.' The equation for sthe :calculation of lthezzinitial f Hence the following quantities. are required .fonthe production oflt leonite:

0.491r potassium chloride with 7.0%NaCl, 1.5202 Epsom salt and 0.276t water.

' .The initial .productsnecessary for" the-conversion are .stirred at a temperature of about 4550..until thewhole ofthe Epsom salt has ybeen dissolved, whichghappens after half anhour, thenvtheimixture is cooled downY to about 25 i C. andthe leoniteisseparated fromthe conversion liquor` by` filtration. `The, K2O-yie1d is 89.11%, thegSO4 yield is 88.4%

.Example 3 As mentioned above, itV is Ysutab1e-to carry out-..the

process of producing double,I salt in two stages, as a much more coarsely granulated crystal product is formed, and, furthermore, becausezthe separation of the liquid containing a large amount of.magnesium chloride from the double salt is much. easier technically at..the second concentrated stage. In theexample here. indicated, a conversion liquor poor in magnesium chloridev "taken from the firststage'of the conversion is tobefusedjThecomposition of this liquor which is saturated"vlzithxNaClv is. as follows: y

. YThe density-of this .solution is 1.295. yconversion is to be carried .out withl Epsomsalt eand pure .potassium chloride, producing leonite. A1 conversion `liquor"`of-the tion `for the: calculation. ofe the; quantitative.. conditions; to

- -.be vapplied is as*v follows:

The productionof 1t. leoniterequires:

1.60m.3 initial liquor, 0.4111" KCl and 1.472t Epsomysalt.

2.24 m.3 ofconversionliquor are formed. v The leonite contains 1.8% NaCl. The yields of ,K2 andof'SOL; lfor the entireprocess are exactly. the =sameas vin,;Exarnple 2,

butfor the partof` the `process calculated.: here.' the yield of K2 is 78.2%, that of S04 is 77.0%. The conversion is carried out by stirring the'initial liquor withV the indicated quantities of potassium kchl'oi'ide and' Epsomsalt at a temperature `of'about"45`50' C. untill'the'whole of Afterwards the mixture is cooled down to' abou't"2`5" C. and the segregatedleonite` is' separatedfromthe mother liquorby iiltration.

Example 4 Production of leonite from potassiumchloride containing NaCl andl `dehydrated magnesium sulfate, v"using a mother liquor of double sulfate free frorn'NaCl and'with a low content 'of MgCl2, originating from a conventional process for the production' of schoenite:

" "The composition of' the initialfliquor is-to be;

11 The density of the liquor is 1.266. The equation for the calculation of the quantities to be applied is as follows:

The conversion liquor resulting from this process corresponds to the solution L25 in accordance with Fig. 2; it is therefore saturated with KCl, NaCl, Epsom salt, and leonite at a temperature of 25 C.

From the above equation results:

The initial quantites rrequired for the production of 1t leonite accordingly are: 3.976 m initial liquor, 0.227t potassium chloride containing NaCl with 58.3% NaCl, 0.6834t MgSO4 (free from water). The quantity of conversion liquor obtained is 3.770 m.

The initial liquor is stirred with the dehydrated magnesium sulfate at about 35-40 C. When the magnesium sulfate is dissolved, the heat of hydration which is set free increases the temperature to about 60 C. After about minutes, the whole of the magnesium sulfate is dissolved. The mixture is then cooled down to about 45-50 C., and the potassium chloride containing sodium chloride is added. The conversion takes about half an hour. Afterwards the mixture is cooled down to a nal temperature of 25 C., for which the quantitative conditions have been calculated, and the segregated leonite is separated from the motor liquor by filtration. When this process is carried out under practical conditions, conversion liquors are formed which correspond very closely to the composition of equilibrium solutions as it is theoretically required (see Table l).

Table 2 indicates a serie of conversion solutions produced by practical application, which have been obtained according to the methods illustrated by the above examples.

TABLE 2 Temperature of Contents of conversion Theoreti- No. Production NaCl in the cal equiof conversion llbrlum liquor Begin- End, solution ning, C. C.

schoenite-.. 40 25 Mn do--.-.. Saturated--. 40 25 M'u Leonlte 60 30 Lm ..--do Saturated.-- 45 25 L'u dodo 45 25 Lu ---.-do dO 45 25 L'zs COMPOSITION OF THE CONVERSION LIQUOB. OBTAINED The double sulfates of potassium and magnesium are important fertilizer materials. As it is known, several plants do not agree with fertilizers containing chlorine. Therefore it is necessary, to oier to these plants the nutritive material potassium in a form free of chlorine. Compared to potassium sulfate-the common form of potassium fertilizer free of chlorine-the double sulfates 12 of potassium and magnesium, as they are given by schoenite or lenoite, contain in addition magnesium, which is also a valuable nutritive component.

In the claims, when the phrase at least meta-stable equilibrium is employed, the same means either metastable equilibrium or stable equilibrium.

I claim:

1. A process for the production of double salts of one mol potassium sulfate and one mol magnesium sulfate having chemically bound water with the recovery of a double salt conversion solution having a high magnesium chlorides content, which comprises contacting a member selected from the group consisting of unhydrated magnesium sulfate and the hydrated magnesium sulfates with potassium chloride at a temperature between about 30 and 55 C. in an aqueous medium to thereby precipitate the double sulfate, said contact solution being prepared by addition of said group member and potassium chloride in such quantities to said aqueous medium that in said contact solution there results concentrations which are adjusted to form at a predetermined lower temperature between 20 and 35 C. a solution in a meta-stable equilibrium, thereaftercooling the contact mixture while precipitating further quantities of the double sulfate, at about said predetermined lower temperature and recovering the double sulfate formed and a mother liquid containing at least 220 grams and up to 285 grams of magnesium chloride per liter.

2. A process in accordance with claim 1 in which said potassium chloride and said group member of the hydrated magnesium sulfates are contacted in water at a temperature between about 30 and 45 C., in which cooling is effected to a temperature between about 20 and 28 C. and in which the recovered double sulfate is the K3SO4 MgSO 6H3O (schoenite) 3. A process in accordance with claim 1 in which said potassium chloride and said group member of the hydrated magnesium sulfates are contacted in water at a temperature between about 45 and 55 C. in which said cooling is effected to a temperature between about 25 and 32 C. and in which the recovered double sulfate is K2SO4'MgSO44H2O (leoniie).

4. A process in accordance with claim 1 in which said potassium chloride and said group member of the hydrated magnesium sulfates are contacted in water, in the added presence of sodium chloride at a temperature between about 30 and 40 C., in which said cooling is effected to a temperature between about 20 and 28 C. and in which the recovered double sulfate is schoenite.

5. A process in accordance with claim 1 in which said potassium chloride and said group member of the hydrated magnesium sulfates are contacted in water, in the added presence of sodium chloride at a temperature between about 45 and 50 C., in which said cooling is elected to a temperature between about 25 and 32 C., and in which the recovered double sulfate is leonite.

6. A process in accordance with claim 1 in which said potassium chloride and said group member of the hydrated magnesium sulfates are contacted in an aqueous solution having an initial content of magnesium chloride, potassium chloride and magnesium sulfate at a temperature between about 40 and 45 C., in which said cooling is effected to a temperature between about 20 and 28 C., in which the recovered double sulfate is schoenite.

7. A process in accordance with claim 1 in which said potassium chloride and said group member of the hydrated magnesium sulfates are contacted in an aqueous solution having an initial content of magnesium chloride, potassium chloride and magnesium sulfate, at a temperature between about 45 and 55 C., in which said cooling is effected to a temperature between about 25 and 32 C., in which the recovered double sulfate is leonite.

8. A process in accordance with claim 1 in which said potassium chloride and said group member of the hydrated magnesium sulfates are contacted in an aqueous solution having an initial content of magnesium chloride, potassium chloride and magnesium sulfate, in the added presence of sodium chloride at a temperature between about 30 and 40 C., in which said cooling is etected to a temperature between about 20 and 28 C., and in which the recovered sulfate is schoenite.

9. A process in accordance with claim 1 in which said potassium chloride and said group member of the hydrated magnesium sulfates are contacted in an aqueous solution having an initial content of magnesium chloride, potassium chloride and magnesium sulfate in the added presence of sodium chloride at a temperature between about 45 and 50 C., in which said cooling is eiected to a temperature between about 25 and 32 C., and in which the recovered double sulfate is leonite.

10. A process in accordance with claim 1 which includes dissolving unhydrated magnesium sulfate in water at a temperature between about 35 and 40 C., whereby the solution takes on a higher temperature by the heat of hydration of the magnesium sulfate, cooling this solution from this higher temperature to a temperature between about 45 and 55 C. adding then said potassium chloride to the cooled solution whereby leonite will be precipitated, and thereafter cooling the mixture thus obtained further to a temperature between about 25 and 32 C. whereby further quantities of leonite will be precipitated and recovering all the precipitated leonite.

11. A process in accordance with claim 10, in which said initial cooling is effected to a temperature about 45 and 50 C., `and which includes the added presence of sodium chloride in the solution of potassium chloride and magnesium sulfate.

l2. A process in accordance with claim 1, which includes dissolving unhydrated magnesium sulfate in an aqueous solution having an initial content of magnesium chloride, potassium chloride and magnesium sulfate between about 35 and 40 C., whereby the solution takes on a higher temperature by the heat of hydration of the magnesium sulfate, cooling this solution from said higher temperature between about 45 and 55 C. adding said potassium chloride to cooled solution whereby leonite will be precipitated and cooling the mixture thus obtained to a temperature of about 25 and 32 C. whereby further quantities of leonite will be precipitated and recovering all the precipitated leonite.

13. A process in accordance with claim 12, in which said initial cooling is effected to a temperature between about 45 and 50 C. and which includes the added presence of sodium chloride in said aqueous solution.

14. A process in accordance with claim 1, which includes dissolving unhydrated magnesium sulfate in an aqueous solution having an initial content of magnesium chloride, potassium chloride and magnesium sulfate between about 35 and 40 C., whereby the solution takes on a higher temperature by the heat of hydration of the magnesium sulfate, cooling this solution from said higher temperature to a temperature between about 30 and 45 C. adding said potassium chloride to cooled solution 14 whereby schoenite will be precipitated and cooling the mixture thus obtained to a temperature of about 20 and 28 C. whereby further quantities of schoenite will be precipitated and recovering all the precipitated schoenite.

l5. A process in accordance with claim 14, in which said initial cooling is effected to a temperature between about 30 and 45 C. and which includes the added presence of sodium chloride in said aqueous solution.

16. A process according to claim 1, which includes as aqueous medium a solution having an initial content of magnesium chloride, potassium chloride and magnesium sulfate, e.g. a conversion solution which contains only a relatively low content of magnesium chloride, produced by the production of double salts of one mol potassium sulfate and one mol magnesium sulfate having chemically bound water by double salt conservion in a well-known manner. i 17. A process in accordance with claim 16, which includes as aqueous solution a conversion solution which contains no more than about 38-45 mols of magnesium chloride for each thousand moles of water.

18. A process in accordance with claim 1, in which, after cooling this contact solution to above said predetermined lower temperature between 20 and 35 C., said double sulfate is separated from said solution at said temperature and which includes further cooling the remaining salt conversion solution to a temperature between about 25 and 10 C. for the precipitation of potassium chloride and a hydrated magnesium sulfate therefrom, separating the precipitated salts from said solution having a substantially higher content of magnesium chloride.

19. A process in accordance with claim 18, in which the salts precipitated at a temperature between about 25 and 10 C. are recycled for further use in said process. 20. A process in accordance with claim 18, which includes the added presence of sodium chloride in said solution and in which sodium chloride may be precipitated by said further cooling to a temperature between aallalrtiut 25 and 10 C. and removed with said precipitated s s.

21. Aprocess in accordance with claim 20, in which the'precipitated potassium chloride, the hydrated magnesium sulfate and sodium chloride are recycled for further use in said process.

Mellor: Comprehensive Treatise on Inorganic and Theoretical Chemistry, vol. 2, 1922, pages 659-660, Longmans Green and Co., New York, N.Y., vol. 4, 1923, page 340. 

1. A PROCESS FOR THE PRODUCTION OF DOUBLE SALTS OF ONE MOL POTASSIUM SULFATE AND ONE MOL MAGNESIUM SULFATE HAVING CHEMICALLY BOUND WATER WITH THE RECOVERY OF A DOUBLE SALT CONVERSION SOLUTION HAVING A HIGH MAGNESIUM CHLORIDES CONTENT, WHICH COMPRISES CONTACTING A MEMBER SELECTED FROM THE GROUP CONSISTING OF UNHYDRATES MAGNESIUM SULFATE AND THE HYDRATED MAGNESIUM SULFATES WITH POTASSIUM CHLORIDE AT A TEMPERATURE BETWEEN ABOUT 30 AND 55* C. IN AN AQUEOUS MEDIUM TO THEREBY PRECIPITATE THE DOUBLE SULFATE, SAID CONTACT SOLUTION BEING PREPARED BY ADDITION OF SAID GROUP MEMBER AND POTASSIUM CHLORIDE IN SUCH QUANTITIES TO SAID GROUP MEDIUM THAT IN SAID CONTACT SOLUTION THERE RESULTS CONCENTRATIONS WHICH ARE ADJUSTED TO FORM AT A PREDETERMINED LOWER TEMPERATURE BETWEEN 20* AND 35* C. A SOLUTION IN A META-STABLE EQUILIBRIUM THEREAFTER COOLING THE CONTACT MIXTURE WHILE PRECIPITATING FURTHER QUANTITIES OF THE DOUBLE SULFATE, AT ABOUT SAID PREDETEMINED LOWER TEMPERATURE AND RECOVER ING THE DOUBLE SULFATE FORMED AND A MOTHER LIQUID CONTAINING AT LEAST 220 GRAMS AND UP TO 285 GRAMS OF MAGNESIUM CHLORIDE PER LITER, 